Many process control systems use pressure regulators to control the pressure of a process fluid, to control a pressure applied to a process control device (e.g., an actuator), etc. Pressure reducing regulators are commonly used to receive a relatively high pressure fluid source and output a relatively lower regulated output fluid pressure. In this manner, despite the pressure drop across the regulator, a pressure reducing regulator can provide a relatively constant output fluid pressure for a wide range of output loads (i.e., flow requirements, capacity, etc.).
Some pressure reducing regulators commonly referred to as dome-loaded pressure reducing regulators utilize a dome or pilot stage that receives a control pressure (e.g., a setpoint pressure or desired output pressure). The control pressure in the dome or pilot stage typically drives a sensor (e.g., a piston) which, in turn, drives a valve stem and its plug against a bias spring toward or away from a valve seat so that the output pressure of the regulator substantially equals the control pressure.
However, such dome-loaded regulator designs typically use a separate piston or sensor and valve plug/stem assembly. Due to the separate piston and valve plug/stem assemblies, these types of regulators are prone to overshooting/undershooting a target output pressure and/or may produce an oscillating output pressure. In particular, because the piston is not mechanically joined to the valve stem, the piston can separate from the valve stem/plug assembly resulting in a transitory or momentary loss of control over the position of the plug relative to the seat. As a result, these types of pressure reducing regulator designs may produce unstable (overshooting, undershooting, oscillating, etc.) output pressures in response to rapid changes in the dome pressure (i.e., the control pressure). For example, in some known applications, control pressure or dome pressure is supplied or controlled via fast acting solenoid valves, which produce rapid pressure changes in the dome and, thus, aggravate the above-described stability problem associated with these known dome-loaded regulators. In addition to the stability issues associated with known dome-loaded pressure reducing regulator designs, the above-described dome-loaded pressure reducing regulators utilize a relatively large number of parts, which tends to increase the material and maintenance cost of the regulators as well as the likelihood of regulator failure.
A pressure reducing regulator having relatively few moving parts and a substantially unitary piston or sensor and valve plug assembly is described in U.S. Patent Publication No. 2004/0007269, the entire disclosure of which is incorporated herein by reference. The pressure reducing regulator described in this patent application publication is an in-line pressure reducing regulator that does not utilize a pilot stage or dome to control output pressure and, instead, uses springs to establish a predetermined output pressure. In addition to reducing the number of moving parts, the substantially unitary piston or sensor and valve plug assembly also eliminates the possibility of the valve plug from separating from the piston/sensor, as can occur with the dome-loaded regulator designs noted above.
Still further, in some applications it is desirable to provide multiple pressure outputs (which may be different pressure values) derived from a single source pressure. Commonly, such multiple output pressure applications are implemented by fluidly coupling two or more pressure reducing regulator assemblies, such as the dome-loaded regulators described above, via a manifold and/or tubing. However, such multiple output regulator assemblies are typically expensive to assemble, bulky, heavy, difficult to maintain, etc.